EFFECT OF PREHEATING IN CARBONIZATION ON THE NATURE OF RESULTANT COAL TARS AND PITCHES

The tars and resultant pitches produced by normal (wet) and preheated carbonization of a high-volatile bituminous coal in a semi-industrial scale coke oven have been compared using a combination of liquid chromatographic (LC) and nuclear magnetic resonance (NMR) spectroscopic methods. The toluene-soluble (TS) and quinoline- (QI) and toluene-insoluble (TI) fractions were selected to assess the differences in composition. HPLC revealed that preheating gave rise to tars containing lower proportions of substituted polynuclear aromatic compounds (PACs) than those produced from the wet coal charge. Pitches derived from the tars obtained with preheating contain more higher molecular weight species as reflected in the higher QI, TI, and asphaltene contents, together with a higher proportion of peri-condensed PACs in the TS fractions. Similarly, solid state C-13 NMR has indicated that the QI and TI fractions from the pitches obtained from the preheated charges contain more highly condensed aromatic structures; limitations with cross polarization (CP) can be largely overcome using the single pulse excitation (SPE) technique.